1. Field of the Invention
The present invention relates to a novel co-generated power supply system, which is useful for co-generated power supply of a combination of natural energy and stable energy such as a fuell cell and power storage energy during the nighttime and midnight, and especially, which can efficiently supply electric power to a load by connecting a plurality of AC and DC energy sources to each other via an electronic transformer, a diode and an OR circuit.
2. Description of the Related Art
As a typical example of clean energy, the solar cell has been prevalant. Furthermore, the wind turbine generator has been introduced in local regions. Since in these types of natural energy, the duration of sunshine, the operation rate of a windmill or generated electric power fluctuates at all times due to variations in weather or meteorological situations, it is difficult to stably supply electric power. Therefore, natural energy is used as an auxiliary energy source while commercial electric power is mainly used in many cases under current circumstances.
However, an electric power supply system in the 21st century in which global warming is suppressed has been studied in a global scope, and thus, various types of efficient electric power supply means by co-generated power supply in closer touch with a consumption region have been studied in addition to conventional concentrated power generation by nuclear energy, thermal energy or hydraulic energy.
Moreover, in order to perform loadleveling, it is necessary to store surplus energy from a commercial AC line in a battery during nighttime and release this energy for use during daytime so as to efficiently actuate a power generation and distribution system even in the above-described conventional concentrated power distribution systems.
In the meantime, in the field of power electronics, there has been developed an electronic transformer compatible with both AC and DC, which could not achieved by a conventional copper-iron type transformer, and therefore, the electric power can be converted irrespective of the AC and the DC of the energy source. Consequently, the AC power, such as from a commercial power source or wind turbine generation, is combined with the DC power, such as from a solar cell, a fuel cell or a battery, for storing midnight electric power via the electronic transformer, and then, the AC power and the DC power can be used at home, in an office or the like as an uninterruptible power supply for allowing instantaneous power interruption within a half cycle by switching over the energy sources.
Examples of household electric appliances which are currently prevalent in Japan and can be securely used for both of AC and DC include a light bulb, an inverter type fluorescent lamp and an electric tool, and further, there can be used, in principle, inverter types of an air-conditioner, a refrigerator, a microwave oven, a vacuum cleaner, a personal computer and a facsimile except for some types in which a voltage doubler rectifying circuit or an AC protective circuit is incorporated. In contrast, a dimmer, a space heating appliance and an automatic rice cooker of a thyristor phase control system cannot be used with DC under present circumstances. As a consequence, there has arisen an immediate inconvenience that the appliance only for AC and the household electric appliance for both of AC and DC must be used with separate indoor wiring systems (i.e., receptacles) independent of each other.
However, the DC power generation energy always is reversely converted into the commercial AC through an inverter in the conventional system, and then, is converted into the DC again within an actual load, and further, is converted into a high frequency inverter or a variable frequency AC power, so as to drive an electric motor or a compressor, thereby increasing a conversion loss.
FIG. 1 is a diagram illustrating the classification of suitability of AC and DC power supply of conventional household electric appliances in a low-tension power distribution system in the case where AC and DC energy sources are used in a co-generated power supply system, and the relationship between the suitability and conversion efficiency. For example, η1, η2 and η3 represent the efficiency in the case where a fluorescent lamp is lighted by the solar cell; and η1, η2, η3 and η4 represent the efficiency in the case where a personal computer or a facsimile is operated.
FIG. 2 is a diagram illustrating a conventional example of a solar cell and a wind turbine generator in a low-tension power distribution system in the case where electric power is supplied directly to a load from AC and DC energy sources. As illustrated in FIG. 2, in the prior art, electric power is supplied directly to both a commercial AC power source and a load via a system linking inverter (popularly called a power conditioner) in the solar cell; in contrast, in the wind turbine generator, since the time fluctuations in generated electric power are sharp, the generated electric power is stored in a storage battery, and then, systems are linked via a bidirectional converter having both of electric charging and discharging functions. In this manner, the solar cell and the wind turbine generator have been configured in systems independent of each other. As to the solar cell, an effective power generation time during the daytime ranges from 6 hours to 8 hours even on a bright day. In contrast, although a weekly or monthly rate of a power generation time in the wind turbine generator greatly depends on seasons or regions, the average rate of the power generation time in Japan is assumed to be smaller than the rate of the power generation time in the solar cell. This is a factor in why the solar cell and the wind turbine generator have not been as prevalent in comparison with in Europe or the U.S.
If control equipment such as an inverter is provided for each electric power of the energy generating source of a low operating rate in the above-described manner, the cost of the entire system is increased, thereby leading to one factor of inhibition of popular use.